Objectives：Marine carbonate rocks is the original recorder and preserver, the chemical constitution of which may approximatively represent the chemical constitution of paleoseawater. However, as for the ancient marine carbonate rocks, which have undergone a series of process, such as deposition, burial process and diagenesis, whether it could have preserved the chemical information of paleoseawater or not, it’s a contentious issues. This paper has carried out a series of work to discuss this issue.Methods:This paper, based on marine carbonates and calcareous shales of Ordovician—Silurian boundary, has studied the ΣREE value, Y/Ho ratio value, Er/Nd ratio value, Mn/Sr ratio value, and the correlation of δEu , REE and δCe by major elements analysis, trace elements analysis and rare earth elements analysis. In this paper, there are two aspects has been discussed, including the influence of the input of terrestrial detrital components and the degree of diagenetic alteration on the preserve of the chemical information of paleoseawater.Results:The content of metallic oxides in limestones and clayshales of the Ordovician—Silurian is stable. The content of CaO in limestones is higher, which is distributed in 36.64%~47.11%. However, compared with modern seawater, the component content of clayshales is similar to PAAS standard values. The ∑REE value of limestones of the Ordovician—Silurian is low. It shows that light rare earth element is enriched and the heavy rare earth element is defective. The Y/Ho value is similar to the value of modern seawater. The Er/Nd averate value is less than 0.1, and Mn/Sr ratio values are lower than 2, and most of ratios are spread from 0.4 to 1.2. The correlation between δEu and δCe is not obvious, and the correlation between REE and δCe is low.Conclusions:Limestones and calcareous shales of Ordovician—Silurian boundary have low diagenetic alteration, and terrigenous matters have less effect on the conservation of the paleoseawater information. This is a reliable preparation for researches by multiple analysis and different angles. So it can provide a new reference for some other areas’ and periods’ researches on paleoseawater information preservation.